This invention relates in general to beam forming architecture, and more specifically to systems and methods for providing controlled selection of areas in which particular signals are transmitted and/or received using either a multiple fixed beam array or an adaptive array.
In a spread spectrum CDMA system, multiple communication units, or mobile systems, operate on a single frequency separated only by a particular CDMA code and/or a CDMA code delay defining a CDMA channel. Typically these CDMA channels are available throughout a cell, or sector of the cell. However, radiation of a CDMA channel within an area of the cell in which the particular communication unit assigned to the CDMA channel is not operating only serves to increase the interference energy experienced by other communication units operating on that frequency.
In order to provide separate communications over a same frequency, a CDMA system must be able to despread and separate the transmitted and received signals that are using different codes or different code delays. Accordingly, CDMA communications are interference limited. If radiation of a particular CDMA channel could be restricted to only within an area most likely to actually be utilized by a communication unit assigned to the CDMA channel, communication capacity may be increased. In order to isolate transmission of a CDMA channel to a particular area within the cell, a multi-beam or adaptive array antenna system is preferably utilized.
Accordingly, there exists a need in the art for a system and method for equipping a CDMA or other base station to dynamically restrict communication with communication units to selected areas to reduce interference. For example, a multiple fixed beam antenna, such as provides substantially non-overlapping antenna beams illuminating a service area, may be switchably connected to transceiver apparatus in order to allow transmission and reception of a CDMA signal within a particular area and transmission and reception of another CDMA signal within another particular area.
However, the use of such switched beam systems sometimes presents a disadvantage in that a cusping point exists between ones of the antenna beams. Such a cusping point provides an area of signal gain reduction or loss. Where this cusping loss is significant, such as on the order of 3 dB gain difference between the cusping point and the center of the beam, communication quality may degrade as a mobile subscriber unit moves from an area near the center of one fixed antenna beam toward the area near the center of another fixed antenna beam, thereby traversing a cusping area there between.
The effects of these cusping loses may be decreased by providing additional fixed beams to thereby provide antenna beam centers which are located more closely together. However, such a solution generally requires prohibitive costs in that the antenna array must be changed and a more complex beam forming matrix must be provided in addition to providing additional circuitry to accommodate the additional number of signals transmitted or received from the added antenna beams.
Adaptive arrays, providing steerable antenna beams which may be controlled to individually point at a current mobile position, may be utilized in avoiding the above described cusping losses and/or other disadvantages associated with fixed antenna beams. Additionally, adaptive beam forming techniques may be utilized not only to provide an antenna beam which best serves the subscriber unit of interest, but such beams may also be formed to reduce interference to/from other units. For example, nulls may be steered in the antenna beam where a source of interference is located in order to avoid or mitigate interference in communications with a subscriber unit of interest.
However, the use of adaptive array antennas generally require the real time determination of complex weighting information and its application to a plurality of signal components used in forming the antenna beam. Such weighting information determination and application generally requires substantial processing resources to provide real time antenna beam steering and can result in signal processing delays or other undesired consequences.
Accordingly, a need in the art exists for a system and method adapted to control the transmission and/or reception of signals to reduce the interference level within a service area wile avoiding cusping losses and/or the need for intensive processing capability in beam forming.
A further need exists in the art for a system and method adapted to operate with a multiple beam array, an adaptive array, or a combination thereof.
These and other objects, features and advantages are achieved in a system and method utilizing a beam forming architecture adapted for both adaptively forming antenna beams having desired attributes as well as selectively switching between antenna beam signals of predetermined antenna beams. Accordingly, utilizing a multi-beam antenna array and a hybrid beam switching and adaptive beam forming technique, the present invention allows for the selection of particular fixed beams suitable for providing the desired communications and the formation of additional antenna beams to redress undesired communications attributes associated therewith, such as cusping losses. Likewise, utilizing an antenna array adapted for adaptive beam forming and a hybrid selectable adaptive beam forming technique, wherein complex signal weighting information associated with various adaptively formed beams are predetermined, disadvantages associated with the computational resource requirements and/or signal processing delays of typical adaptive array systems are redressed.
A preferred embodiment of the present invention operates to take the inputs from a multi-beam antenna, such as a twelve beam antenna system, and switch ones of those beams so that the best beams, the preferred embodiment switching six such beams, are routed into the cell site demodulator. Where the signal quality or other communication attribute associated with the antenna beams provided by the antenna array is undesirable, the present invention preferably utilizes ones of the antenna beam signals to adaptively, i.e., applying adaptive beam forming weighting and combining such as linear coherent complex combining, form antenna beam signals having an improved communication attribute. For example, where a subscriber mobile unit is disposed at a cusping point between two of the antenna beams provided by the multi-beam antenna, the present invention may operate to form an antenna beam substantially centered at this cusping point to provide better communication attributes.
A preferred embodiment of the present invention operates to take the inputs from an antenna array having antenna elements disposed in a configuration suitable for antenna beam forming, such as a twelve antenna element column antenna system, and form desired antenna beams therefrom, switching ones of, or otherwise providing, those beams so that the best beams, the preferred embodiment switching six such beams, are routed into the cell site demodulator. Preferably, to reduce the burden on processing resources required to provide beam forming, various predetermined sets of signal component weighting information are utilized which correspond to antenna beams commonly used. Where the signal quality or other communication attribute associated with the antenna beams provided by the antenna array, the present invention preferably adaptively forms antenna beam signals having an improved communication attribute in addition to the predetermined sets of weighting information.
According to a most preferred embodiment of the present invention, a multifarious beam forming architecture is adapted for use with either a fixed antenna beam array, an adaptive array, or a combination thereof. Accordingly, a common architecture may be utilized in both the multi-beam antenna and adaptive antenna array embodiments described above by providing information with respect to the signals provided by a coupled antenna to allow for proper beam forming according to the present invention. Moreover, by coupling the inventive architecture to both a beam forming matrix of a multi-beam antenna array and the antenna elements associated therewith, the architecture may be utilized in providing a combination of the above described embodiments. For example, beam switching supplemented by adaptive beam forming using a multi-beam array may be performed on the reverse link while adaptive beam forming utilizing predetermined sets of weighting parameters using an adaptive array antenna may be performed on the forward link.
A technical advantage of the present invention is provided in that disadvantages associated with the use of a fixed beam array are addressed utilizing a hybrid beam switching technique including beam adaptive forming capabilities to provide antenna beams having desired attributes to supplement those associated with the fixed beam array.
A further technical advantage of the present invention is provided in that disadvantages associated with the use of an adaptive array are addressed utilizing a hybrid adaptive beam forming technique with predefined beam switching or selection capabilities to ease the burden of fully adaptively forming all desired antenna beams.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.